A known liquid ejection apparatus, e.g., an inkjet head, is configured to eject ink from nozzles thereof. The inkjet head includes a channeled substrate including a plurality of pressure chambers and a piezoelectric actuator provided on the channeled substrate. Each of the pressure chambers of the channeled substrate communicates with a corresponding one of the nozzles and has a rectangular shape. In other words, each of the pressure chambers has a longitudinal direction. The pressure chambers are arranged along a transverse direction orthogonal to the longitudinal direction.
The piezoelectric actuator includes a vibration plate and a plurality of piezoelectric elements. The vibration plate is formed of, for example, silicon dioxide, and covers the pressure chambers. The piezoelectric elements are provided on the vibration plate in correspondence with the pressure chambers. Each of the piezoelectric elements includes a piezoelectric film, a lower electrode located below the piezoelectric film, and an upper electrode located above the piezoelectric film.
The lower electrode is an individual electrode individually provided for each pressure chamber. The lower electrode is disposed on the vibration plate, overlapping a central portion of the pressure chamber in its transverse direction. The upper electrode is disposed overlapping almost the entire area of the pressure chamber with respect to its transverse direction. The upper electrodes are electrically connected to each other between the piezoelectric elements, and the same potential is applied to the upper electrodes. The upper electrodes constitute a common electrode shared among the piezoelectric elements.
A portion of the piezoelectric film between the lower electrode and the upper electrode is an active portion configured to deform when a voltage is applied between the two electrodes. As described above, the upper electrode overlaps the almost entire area of the pressure chamber with respect to its transverse direction. Accordingly, a position of each end of the active portion with respect to the transverse direction is determined by a position of a corresponding end of the lower electrode.